An in situ digital background calibration algorithm for multi-channel R-βR ladder DACs

The R-2R resistor ladder is one of the best topologies for implementing compact-sized digital-toanalog converter (DAC) arrays in implantable neuro-stimulators. However, it has a limited resolution and considerable inter-channel variation due to component mismatches. To avoid losing analog information, we present sub-radix-2 DAC implemented by the R-βR resistor ladder in this paper. The digital successive approximation register (DSAR) algorithm corrects the transfer function of DACs based on their actual bit weights. Furthermore, a low-cost in situ adaptive bitweight calibration (ABC) algorithm drives the analog output error between two DACs to zero by adjusting their bit weights automatically. The simulation results show that the proposed algorithm can calibrate the non-linear transfer function of each DAC and the gain error among multiple channels in the background.